linux-kernel - Re: [PATCH V8 4/5] i3c: master: Add endianness support for i3c_readl_fifo() and i3c_writel_fifo()

Open Source and information security mailing list archives

Message-ID: <aNaod76qkM4Srqyl@lizhi-Precision-Tower-5810>
Date: Fri, 26 Sep 2025 10:51:35 -0400
From: Frank Li <Frank.li@....com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Manikanta Guntupalli <manikanta.guntupalli@....com>, git@....com,
	Michal Simek <michal.simek@....com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Rob Herring <robh@...nel.org>, krzk+dt@...nel.org,
	Conor Dooley <conor+dt@...nel.org>,
	Przemysław Gaj <pgaj@...ence.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	tommaso.merciai.xr@...renesas.com, quic_msavaliy@...cinc.com,
	Shyam-sundar.S-k@....com,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	"'billy_tsai@...eedtech.com'" <billy_tsai@...eedtech.com>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Jorge Marques <jorge.marques@...log.com>,
	"linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-hardening@...r.kernel.org, radhey.shyam.pandey@....com,
	srinivas.goud@....com, shubhrajyoti.datta@....com,
	manion05gk@...il.com
Subject: Re: [PATCH V8 4/5] i3c: master: Add endianness support for
 i3c_readl_fifo() and i3c_writel_fifo()

On Fri, Sep 26, 2025 at 01:09:37PM +0200, Arnd Bergmann wrote:
> On Fri, Sep 26, 2025, at 12:53, Manikanta Guntupalli wrote:
> > Add endianness handling to the FIFO access helpers i3c_readl_fifo() and
> > i3c_writel_fifo(). This ensures correct data transfers on platforms where
> > the FIFO registers are expected to be accessed in either big-endian or
> > little-endian format.
> >
> > Update the Synopsys, Cadence, and Renesas I3C master controller drivers to
> > pass the appropriate endianness argument to these helpers.
> >
> > Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@....com>
> > Reviewed-by: Frank Li <Frank.Li@....com>
>
> I don't think this is a good interface, based on our discussion
> so far, and I had hoped you'd change it the way I had suggested
> with a separate function for the xi3c driver, so normal drivers
> don't have to worry about the AMD specific quirk.
>
> I think this should also avoid mentioning "endianess" in the
> changelog and in the code itself, since that would likely
> confuse readers into thinking (as I did in my earlier replies)
> that this is related to using big-endian kernels.
>
> i3c_readl_fifo()/i3c_writel_fifo() are already portable and
> handle endianess correctly by using the readsl()/writesl()
> functions.

I agree. I think previous your suggested API is good.

/*
 * BIT: 31..24   23..16  15..8   7..0
 *       B0       B1       B2    B3
 *
 * Memory:
 *  0x0:  B0
 *  0x1:  B1
 *  0x2:  B2
 *  0x3:  B3
 */
i3c_writel_fifo_bytereversed()

Frank
>
>     Arnd
>
> --
> linux-i3c mailing list
> linux-i3c@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-i3c

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives